Predicting streamflow response to increased imperviousness in an urbanizing watershed using an integrated modeling approach

Background/Question/Methods

Hinkson Creek Watershed (HCW) is an urbanizing watershed in central Missouri comprising an area of 234 km2. Approximately 59% of Columbia, a city of 113,225 residents, is situated within HCW. In 1998, Hinkson Creek was listed as impaired under section 303(d) of the Clean Water Act. This designation led to the development of a volume-based TMDL plan by the Environmental Protection Agency (EPA) and Missouri Department of Natural Resources in 2011. Urban growth in HCW has been rapid; between 2000 and 2012, the population of Columbia increased by 30.6% and, between 1980 and 2000, total impervious surface cover in HCW increased from 5.9% to 8.2%. To assess how increasing imperviousness will affect the timing and amount of Hinkson Creek’s streamflow, the Imperviousness Change Analysis Tool (I-CAT), a GIS-based urban growth model, has been used to simulate the amount of impervious surface cover in Boone County, Missouri to the year 2030. Results derived from I-CAT were coupled with the Soil Water Assessment Tool (SWAT), a semi-distributed hydrologic model, to quantify changes to Hinkson Creek’s streamflow regime. This coupled modeling process is designed to provide quantitative management information for HCW and can also be used by decision makers in other urbanizing watersheds.

Results/Conclusions

Preliminary results derived from the urban growth modeling (using I-CAT) show that, at the current rate of growth, the amount of impervious surface cover in HCW is likely to increase from 8.2% (19.1 km²) to at least 11.5%, or 26.8 km², by the year 2030. Stream discharge comparisons were made using current land-cover data versus land-cover data that included the simulated impervious surface growth. Results derived from SWAT suggest that stream discharge could increase by approximately 2.2% annually.